Method for processing output or base signals from a device for determining a distance of an object

ABSTRACT

To provide a method of processing output or base signals (S), in particular intermediate frequency output or base signals, from at least one device, in particular at least one radar device, for determining a distance (d), in particular a small distance on the order of magnitude of approximately zero meters to approximately 7 meters, of an object, by which it is possible to obtain from the raw signals, i.e., the output or base signals, distance information with respect to at least one object located in the detection or sensing range of the device, the following steps are provided:  
     (a) Adaptively determining the background signal (S 0 ) by localized filtering of the output or base signal (S) using at least one localized filter having a specified width (B);  
     (b) Correcting the background of the output or base signal (S) by  
     (b.1) subtracting the determined background signal (S 0 ) from the output or base signal (S) and  
     (b.2) forming a signal, in particular (s=abs (S−S 0 )), for example, from the difference (S−S 0 ) of the output or base signal (S) and the background signal (S 0 );  
     (c) Low-pass filtering, in particular temporal low-pass filtering, of the absolute value signal (s);  
     (d) Forming a correlation signal (k=korr(s)) by correlating, in particular folding, the low-pass filtered absolute value signal (s) with at least one reference maximum having a half-value width; and  
     (e) Determining the at least one object maximum (M) using at least one location-variable, adaptive threshold value (t) which may be determined from the correlation signal (k).

TECHNICAL AREA

[0001] The present invention relates to a method of processing output orbase signals, in particular intermediate frequency output or basesignals, from at least one device, in particular at least one radardevice, for determining a distance, in particular a small distance onthe order of magnitude of the close range of a vehicle, of an object.

BACKGROUND INFORMATION

[0002] In short range radar (SRR) systems, i.e., in radar devices fordetermining an, in particular, small distance, various methods are knownfor processing and evaluating output or base signals. One method, forexample, is based on a threshold value algorithm, taking into account abackground signal which is assumed to be constant, and taking intoaccount distant-dependent, fixed threshold values.

[0003] However, for objects present which are to be detected or sensedby SRR systems and which move at a high relative velocity, this canresult in exceedance of the threshold values at positions where objectsare not present.

[0004] Such phenomena, which may be subsumed under the concept of theparasitic Doppler effect, result in undesired malfunctions and/orerroneous information. Furthermore, malfunctions and/or erroneousinformation may also be caused by intrinsic phenomena such as agingeffects or temperature influences.

DESCRIPTION OF THE INVENTION: OBJECT, ACHIEVEMENT, ADVANTAGES

[0005] Based on the above-mentioned disadvantages and shortcomings, theobject of the present invention is to provide a method of theaforementioned type by which it is possible to obtain from the rawsignals, i.e., the output or base signals, from at least one device, inparticular at least one radar device, distance information with respectto at least one object located in the detection or sensing range of thedevice.

[0006] In this context, the aim of the present invention is to designthe processing of the output or base signals in such a way as tominimize the influence of changes in the output or base signals on thesignal amplitudes to be evaluated with respect to the maximum or peakpositions.

[0007] Consequently, the present invention also aims to provide a methodby which the accuracy of detection may be increased under allconditions.

[0008] This object is achieved according to the teaching of the presentinvention by a method having the features stated in Claim 1.Advantageous embodiments and useful refinements of the present methodare characterized in the subclaims.

[0009] Using the measures according to the present invention, a robustmethod of processing output or base signals from a device fordetermining a distance of an object is provided which is substantiallyindependent of extrinsic effects (for example, a parasitic Dopplereffect when objects having a high relative velocity are present) andintrinsic effects (for example, aging phenomena or temperatureinfluences).

[0010] In this context, one skilled in the art in the field of signalprocessing is aware in particular that complicated modifications orchanges to the system components in the high-frequency part forsuppressing the parasitic Doppler effect or for increasing the accuracyof detection in practically all applications and operational areas, suchas parking aids or pre-crash detection systems, may be dispensed with.

[0011] Lastly, the present invention relates to a device, in particulara radar device, for determining a distance, in particular a smalldistance on the order of magnitude of the close range of a vehicle, ofan object, which operates according to the method described above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Additional embodiments, features, and advantages of the presentinvention are explained in greater detail below with reference to theexemplary embodiment illustrated by FIGS. 1 through 6.

[0013]FIG. 1 shows a diagram in which the typical progression of anintermediate frequency output or base signal at the mixer output of amicrowave detector device is plotted against the distance of the object;

[0014]FIG. 2 shows a diagram in which the typical progression of anintermediate frequency output or base signal at the mixer output of aradar device for a structured background signal is plotted against thedistance of the object;

[0015]FIG. 3 shows a diagram in which the curve is plotted for theintermediate frequency output or base signal according to FIGS. 1 or 2after digital-to-analog conversion;

[0016]FIG. 4 shows a diagram in which the progression of the absolutevalue signal from the difference between the output or base signal andthe background signal is plotted against the distance of the object;

[0017]FIG. 5 shows a diagram in which the progression of the correlationsignal formed by correlating, in particular multiplying, the low-passfiltered absolute value signal according to FIG. 4 by a referencemaximum having a half-value width is plotted against the distance of theobject; and

[0018]FIG. 6 shows a diagram in which the progression of the signal at amaximum, which is determined using a location-variable, adaptivethreshold value that may be determined from the correlation signalaccording to FIG. 5, is plotted against the distance of the object.

[0019] Identical or similar embodiments, elements, or features areprovided with the same reference numbers in FIGS. 1 through 6.

BEST MODE OF IMPLEMENTING THE PRESENT INVENTION

[0020] With reference to FIGS. 1 through 6, one exemplary embodiment isillustrated for a method of processing intermediate frequency output orbase signals S, which may also be described as intermediate frequencyraw signals, using a microwave detector device (see FIG. 1) or a radardevice for a structured background signal S₀ (see FIG. 2).

[0021] Using this method, it is possible to determine distance d of anobject, for example when parking a motor vehicle the distance from thecurb or the distance of the bumper from the motor vehicle parked infront or behind. In this context, using the method according to thepresent invention, in particular small distances in the approximatevicinity of a vehicle, for example from about zero meters to about 30meters, may be determined.

[0022]FIGS. 1 and 2 show typical characteristics of intermediatefrequency output or base signals S (raw signals). These raw signals arepresent in a low-voltage range, in particular in an output voltage rangeof from approximately zero volts to approximately 5 volts, the averagevalue preferably being approximately 2.5 volts. Background signals S₀,i.e., the signals in the absence of objects, have a different averagevalue and a more or less strongly pronounced structure, depending on thetype of sensor device (sampling phase detector device in FIG. 1; radardevice in FIG. 2).

[0023] In this context, the short range radar (SRR) system functions asa sampling phase detector device (a phase-dependent pulse radar device);i.e., the distance maxima are cancelled for the intermediate frequencyas a function of the distance from the object to be detected (see FIG.1); positive and negative maxima each result in cancellations atdistances of one-fourth wavelength (λ/4), in other words, at distancesof approximately 3 millimeters at a carrier frequency of, in particular,approximately 24 Gigahertz.

[0024] Specified portions may be superimposed on intermediate frequencyoutput or base signal S (raw signal) by extrinsic phenomena, such as theparasitic Doppler effect (see FIG. 2), and/or by intrinsic phenomenasuch as aging effects or temperature influences, with the result thatbackground signal S₀ may be very highly structured.

[0025] In the method according to the exemplary embodiment, thedigitalized voltage values of intermediate frequency output or basesignal S from the sampling phase detector device first undergo adigital-to-analog conversion before background signal S₀ is adaptivelydetermined by localized filtering of output or base signal S, using alocalized median filter of a specified width B (see FIG. 1; objectmaximum M marked by the arrow exhibits a “backswing response” at “1” dueto the sampling phase detector device; at “2” the object is displaced byone-half wavelength (λ/2) with respect to “1”; in FIG. 2, object maximumM marked by the single arrow is located on the structured backgroundcaused by the parasitic Doppler effect; fixed, distance-dependentthreshold values are marked by the double arrow).

[0026] To this end, multiple, for example eleven, voltage values foroutput or base signal S are measured at a specified time over thespectrum, sorted, and the median (as the value in the middle of thewindow) is selected, width B of localized median filter being adjustedto the maximum width in output or base signal S for the object (see FIG.3). By this formation of median or average values, object maximum M isidentified (see FIG. 3) and “interfering” maxima are eliminated.

[0027] The background for output or base signal S is subsequentlycorrected. To this end, background signal S₀, determined using thelocalized filtering, is subtracted from output or base signal S, andabsolute value signal s=abs (S−S₀) is formed from difference S−S₀ ofoutput or base signal S and background signal S₀. This absolute valueformation takes into account the fact that the signal amplitude mayfluctuate about the average value due to the properties of the samplingphase detector device, and thus has the advantage that the correction isreliably made even with variable background signals S₀ (for a “fixed”constant background, an overall difference could also be formed).

[0028] To increase the accuracy of detection under all conditions forthe present method, after the background is corrected temporal low-passfiltering is provided for the absolute value signal s produced. To thisend, the positive portions and the negative portions of absolute valuesignal s produced are summed over multiple measurement cycles, thetemporal low-pass filtering being carried out by a floating averagevalue filter having a specified time constant.

[0029] Subsequently, for peak amplification, i.e., for amplifying themaximum according to FIGS. 4 and 5, a correlation signal k=korr(s) isdetermined by correlating, in the case of the present embodiment byfolding, low-pass filtered absolute value signal s with a referencemaximum having a half-value width.

[0030] In the subsequent peak detection, i.e., in the determination ofthe peak locations, object maximum M is determined using alocation-variable, adaptive threshold value t (see FIG. 6) which may bedetermined from correlation signal k (see FIG. 6), location-variable,adaptive threshold value t being acted on by a distance-dependent offsetvalue Δ (see FIG. 6).

[0031] To now obtain the actual distance of the object, the peaklocation, i.e., the position of object maximum M is associated with aspecified distance d of the object using a characteristic curvedetermined through calibration. Consideration should be made for thefact that the relationship between the signal peak and the distance ofthe object or of resolution cells (to be briefly described below) is notlinear, which makes it necessary to determine the calibrationcharacteristic curve.

[0032] This is carried out using resolution cells; i.e., the region fordetermining distance d of the object is subdivided into a specifiednumber of cells, for example into 2⁸=256 cells (8 bits), which in theembodiment of the present method provide reference measurements in 256levels; consequently, it is possible to conveniently determine in whichof the 256 resolution cells the object is located.

What is claimed is:
 1. A method for processing output or base signals(S), in particular intermediate frequency output or base signals, fromat least one device, in particular at least one radar device, fordetermining a distance (d), in particular a small distance on the orderof magnitude of the close range of a vehicle, of an object, having thefollowing steps: (a) Adaptively determining the background signal (S₀)by localized filtering of the output or base signal (S) using at leastone localized filter having a specified width (B); (b) Correcting thebackground of the output or base signal (S) by (b.1) subtracting thedetermined background signal (S₀) from the output or base signal (S) and(b.2) forming a signal, in particular the absolute value signal (s=abs(S−S₀)), for example, from the difference (S−S₀) of the output or basesignal (S) and the background signal (S₀); (c) Low-pass filtering, inparticular temporal low-pass filtering, of the absolute value signal(s); (d) Forming a correlation signal (k=korr(s)) by correlating, inparticular folding, the signal, in particular the low-pass filteredabsolute value signal (s), with at least one reference maximum having ahalf-value width; and (e) Determining the at least one object maximum(M) using at least one location-variable, adaptive threshold value (t)which may be determined from the correlation signal (k).
 2. The methodas recited in claim 1, wherein the output or base signal (S) undergoes adigital-to-analog conversion before the background signal (S₀) isadaptively determined.
 3. The method as recited in claim 1 or 2, whereinthe localized filtering of the output or base signal (S) at a specifiedtime is carried out by measuring, sorting, and selecting the averagevalue from multiple, for example eleven, voltage values over thespectrum.
 4. The method as recited in at least one of claims 1 through3, wherein the output or base signal (S) is locally filtered using atleast one median filter.
 5. The method as recited in at least one ofclaims 1 through 4, wherein the width (B) of the localized filter isadjusted to the width of the object maximum (M) of the output or basesignal (S) for the object.
 6. The method as recited in at least one ofclaims 1 through 5, wherein the absolute value signal (s) is low-passfiltered by summing portions in the absolute value signal (s) over atleast one, in particular over multiple, determination cycles.
 7. Themethod as recited in at least one of claims 1 through 6, wherein thelow-pass filtering is carried out using at least one, in particularfloating, average value filter having a specified time constant.
 8. Themethod as recited in at least one of claims 1 through 7, wherein thelocation-variable, adaptive threshold value (t) is acted on by at leastone distance-dependent offset value (Δ).
 9. The method as recited in atleast one of claims 1 through 8, wherein the object maximum (M) isassociated with a specified distance (d) of the object using at leastone characteristic curve determined by calibration.
 10. The method asrecited in at least one of claims 1 through 9, wherein the range fordetermining the distance (d) of the object is subdivided into aspecified number of cells, for example into 2⁸=256 cells (8 bits).
 11. Adevice, in particular a radar device, for determining a distance (d), inparticular a small distance on the order of magnitude of the close rangeof a vehicle, for example from approximately zero meters toapproximately 30 meters, of an object, which operates according to themethod as recited in at least one of claims 1 through 10.